1. Field of the Invention
The present invention generally relates to an image-reading device, an image-forming device, and a reference-white data creating method, and more particularly, to an image-reading device, an image-forming device, and a reference-white data creating method which perform a white-shading correction.
2. Description of the Related Art
In an image-reading device of a type having a movable image-reading unit represented by a conventional flat-bed type, white-shading data is created by reading a density of a reference-white plate placed within a range in which a carriage moves to an effective read-range limit at an increasing speed. In an image-reading device of a type having a fixed image-reading unit represented by a sheet-through type, white-shading data is created by reading a density of a reference-white plate or a white roller placed on a surface opposite the fixed image-reading unit.
However, in a conventional technology of creating the white-shading data, the surface of the reference-white plate or the white roller is stained as time elapses so that a reference density varies depending on a read range of the reference-white plate or the white roller; this disables maintaining a uniform density necessary for creating the white-shading data. Especially, in the sheet-through type, since a subject copy is conveyed on the surface of the reference-white plate or the white roller, the reference-white plate or the white roller is remarkably stained while being used.
Thereupon, regarding the image-reading device of the sheet-through type, there is a conventional technology of creating the white-shading data based on white data corresponding to a head margin (containing no image) of a subject copy, or based on data of several pixels located at an end part in a main scanning direction on which a subject copy does not pass (and which is not likely to be stained).
In addition, Japanese Laid-Open Patent Application No. 5-319613 discloses a technology in which a groove is formed at a portion of a circumferential surface of a read roller, and a reference-white portion is provided at a bottom portion of the grove for use in a creation of white-shading data so that the reference-white portion is kept from being stained despite the conveyance of a subject copy.
However, the above-mentioned conventional technology of creating white-shading data based on white data corresponding to a head margin of a subject copy has a problem that there is not always a margin in a subject copy. Also, the above-mentioned conventional technology of creating white-shading data based on data of several pixels located at an end part in a main scanning direction on which a subject copy does not pass has a problem that, when the quality of data of pixels in a main scanning direction varies, white-shading data based on white data of some of these pixels cannot contribute to a sufficient white-shading correction.
In addition, in the above-mentioned technology disclosed in Japanese Laid-Open Patent Application No. 5-319613, dust and waste of paper powders and toners produced as subject copies being conveyed are accumulated in the above-mentioned groove which is not easy to clean up. Additionally, a shadow of the groove is formed by a light projected from a light source of a reader portion so as to deteriorate the quality of the read image.